Wireless communication systems have become widely popular in recent years. Advancements in communication technology have permitted the development, and popular usage, of new types of communication devices, of improved performance, portability, and affordability.
In a wireless communication system, a radio communication channel extends between a sending station and a receiving station. The radio channel is defined upon a portion of the electromagnetic spectrum. This communication link between the sending and receiving stations is wireless and can thereby be untethered.
A cellular communication system is exemplary of a wireless, multi-user communication system. Here, several fixed-site base stations are installed to cover a geographical area. By transmitting signals with controlled power, the same frequencies can be re-used at different locations throughout the geographical area. Thereby, communication capacity is maximized power control is at the core of cellular system design.
Various standards have been developed for cellular communication systems. Interim Standard IS-95, promulgated by the EIA/TIA, is exemplary of a standard which pertains to a cellular communication system utilizing CDMA (code-division, multiple access) communication techniques. In a CDMA communication system, several communication signals share a common frequency channel. In such a communication scheme, the power levels of each user must be regulated to achieve optimal capacity. Power control is needed to ensure that none of the signals overwhelm the other signals.
Power control is used to ensure that transmitted communication signals are strong enough to recover the informational content at the receiver, but also low enough to not reduce the communication capacity of the communication channel. Most communications systems utilize closed-loop power control schemes. In the closed-loop power control scheme defined in the IS-95 standard, power control bits are generated and transmitted by network infrastructure on the forward link channel to a radio telephone. These power control bits control the power levels for the reverse link communication signals transmitted by the radio telephone. Therefore, a method is needed to change the power level of the transmitter. Several technical challenges are presented by the power control bit rate and the accuracy requirements of IS95.
Most radio telephones are powered by portable power supplies or batteries. These batteries store limited energy, and therefore need to be replaced or recharged regularly. It is also advantageous to minimize the power requirements of the radio telephone. By reducing the power required to operate the radio telephone, the discharge rate for the stored energy of a battery pack is reduced. Thereby the time period during which a single battery pack can be utilized to power the radio telephone can be increased. That is to say, a technical challenge exists to provide manners by which to increase the "talk time" of the radio telephone with a single battery pack.
The transmitter portion of a radio telephone typically includes a power amplifier. The power amplifier amplifies a reverse link signal prior to its transmission so that it will be received by a base station via a radio channel. A power amplifier requires relatively large amounts of energy for its operation. Conventionally, power amplifiers are powered or biased to accommodate the maximum power levels transmitted by the radio telephone. However, in an IS-95, the typical power levels of reverse link signals are generally significantly less than the maximum power levels.
A manner to provide control of gain and power consumption in a power amplifier is advantageous.
A manner by which to utilize the power amplifier to effectuate power control in a two-way power control scheme is also advantageous.
It is in light of this background information related to transmitter circuits, that the significant improvements of the present invention have evolved.